poor voice quality on phone calls

I get on 75% of my calls that my voice is muffled/ distorted by the recipient. Sometimes when I switch to speaker it helps and sometimes it gets better off speaker. I have never had this problem with any other BlackBerry. Is there any settings or anything I can do to help?

Is this with every call?
I once set my phone to Wi-Fi preferred when making calls. If that is an option for you, make sure you set it to cellular and see how the calls are.
Otherwise, you could try getting assistance from carrier. They "reprovisioned" my phone or whatever they call it, and things did improve. This was my experience with a previous BlackBerry.